From:backyardbob e-mail:somewhere-A-newjersey
Subject:RE: RE: RE: RE: engine locks down and refires Date:Tue Jun 9 17:32:02 2015
Response to:20542
That's usually the case when the clearances are borderline. Two stroke motors, because they have oil in the fuel, are set up to tighter clearances than their four-stroke cousins. Aluminum expands and contracts at a faster rate than cast iron does so it's the piston expanding in the bore under high heat conditions that's locking it up. Racers open up the bore above tolerances for those conditions and when the motor is cold you can hear the piston slap when they first start up. I'm sure there are more experienced people here on the Exchange so if they chime in on this listen then make up your own mind as to which direction you want to go. Either way.... Best of Luck!

BOb, so would the piston free up instantly or would it take time?

Thanks I'll check it out.

Let's assume you don't have a big piece of cardboard blocking the airflow over the engine or a lot of broken fins. Your bore to piston is too tight and it locks when the piston expands in the cylinder. Take it and have the cylinder honed(not bored)another .001" to .0015" (that's a thousandth or thousand and a half inch oversize). The easiest way to tell a 125 from a 165 is if the spark plug is set at an angle it's a 125. If it stands straight up it's a 165. You said 50+ miles an hour? Probably a 165.

New here and with the hummer. I have a 59 and when I ride for a few miles at 50+ mph it will lock down and slide the rear tire. I can immediately pull the clutch in and kick it and fires right back up. If I ride at lower speeds it runs fine with no trouble. Any ideals? I run the 25:1 oil mixture. As I read thru the site it looks like years of experience here. I have already used a lot of info from this site to get it running. Thanks to all !! Also, how do I know if it's a 125 or 165 motor.

Thanks for everything guys